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When your stamping die, injection mold, or mechanical fixture demands consistent, repeatable force under heavy cycling loads, a weak or mismatched spring becomes a costly liability. Engineers, toolmakers, and serious DIY fabricators who need a dependable heavy-load compression die spring will find this JIS-standard range covers the widest selection of outer diameters (6–50 mm / 0.24–1.97 in) and lengths (10–500 mm / 0.39–19.69 in) in a single listing.
Each spring is manufactured to JIS B 5012 heavy-load (red-stripe) specifications. The coil body is formed from high-grade chromium-vanadium alloy steel (Cr-V), shot-peened for fatigue resistance, and finished with a red epoxy coating for corrosion protection. Outer diameters span 6 mm to 50 mm; inner diameters are sized at approximately 50% of OD per JIS convention; free lengths range from 10 mm to 500 mm depending on the OD group selected.
Typical use cases include progressive stamping dies requiring heavy-load return force, plastic injection mold ejector-pin return systems, hydraulic press tooling fixtures, and custom mechanical assemblies where a standard ISO or JIS compression die spring for heavy-duty cycling is specified. The consistent spring rate across the range makes these suitable for load-calculation-critical applications such as blanking dies and deep-draw tooling.
Conforms to JIS B 5012 heavy-load specification — the highest standard deflection-to-load ratio in the JIS die-spring family, delivering maximum force in a compact envelope.
Cr-V alloy coil wire provides superior tensile strength and fatigue life compared to standard carbon steel, sustaining millions of cycles under heavy dynamic loading.
Fourteen outer-diameter groups (6, 8, 10, 12, 14, 16, 18, 20, 22, 25, 30, 35, 40, 50 mm) each paired with multiple free lengths — one listing covers virtually every JIS heavy-load pocket size.
Shot peening induces compressive surface stress to resist crack initiation; the red epoxy topcoat provides corrosion protection and serves as the standard JIS heavy-load color identifier.
Each size is manufactured to a defined spring constant (N/mm), enabling accurate load calculations for blanking, forming, and ejector-return applications without custom engineering.
Both ends are closed and ground flat to ensure square seating in die pockets, preventing lateral deflection and uneven load distribution during press cycling.
| Standard | JIS B 5012 Heavy Load (Red Class) |
|---|---|
| Material | Chromium-Vanadium alloy steel (Cr-V) |
| Surface Treatment | Shot-peened + red epoxy coating |
| End Type | Closed and ground |
| Outer Diameter (OD) | 6 mm – 50 mm (0.24 in – 1.97 in) |
| Inner Diameter (ID) | See variant options |
| Free Length | 10 mm – 500 mm (0.39 in – 19.69 in) |
| Load Class | Heavy (maximum deflection ~30% of free length) |
| Spring Rate | See variant options |
| Operating Temperature | Up to approximately 80 °C (176 °F) continuous |
| Coil Direction | Right-hand wound |
| Color Code | Red (JIS heavy-load identifier) |
Measure the pocket bore in your die plate — the spring OD should be 0.5–1 mm smaller than the bore for clearance. The free length should be selected so that the spring is pre-compressed (typically 10–15% of free length) at the closed position of the die, and does not exceed 30% total deflection at full stroke to stay within the JIS heavy-load working range.
JIS B 5012 heavy-load class springs are rated for a maximum working deflection of approximately 30% of the free length. Exceeding this limit significantly reduces fatigue life. For applications requiring greater deflection, consider the medium-load (blue) or light-load (yellow) class instead.
JIS B 5012 and ISO 10243 define similar but not identical dimensional standards. The OD and ID values are generally close, but spring rates and deflection limits may differ. Always verify the spring rate (N/mm) and pocket dimensions against your tooling drawing before substituting a JIS spring in an ISO-specified application.
Under JIS B 5012, die springs are color-coded by load class: red = heavy load, blue = medium load, yellow = light load, and green = extra-light load. The red epoxy coating on these springs confirms they are the heavy-load class, providing the highest force output per unit of deflection within the JIS family.
Yes. JIS heavy-load compression die springs are widely used in injection mold ejector-return applications. Select an OD that fits your ejector-plate spring pocket and a free length that provides adequate pre-load at the retracted position. Ensure the total deflection per cycle stays within the 30% limit for long service life.
When operated within the JIS-specified deflection range (≤30% of free length for heavy-load class) and at temperatures below 80 °C, Cr-V die springs typically achieve 500,000 to 1,000,000+ cycles. Exceeding the rated deflection, operating at elevated temperatures, or using the spring in a laterally loaded condition will reduce service life significantly.
Light lubrication with a molybdenum-disulfide (MoS₂) grease or a dedicated die-spring lubricant on the OD and ID contact surfaces is recommended for high-cycle applications. This reduces fretting wear between the spring and the guide pin or pocket bore, extending fatigue life. Avoid petroleum-based oils that may degrade the epoxy coating over time.
